1. Field of the Invention
This invention relates to a magnetic recording device and a magnetic recording apparatus in which a radio-frequency magnetic field is applied in combination with a write current.
2. Background Art
Applying a magnetic field is a conventional method for controlling the magnetization direction of a magnetic material. For example, in a hard disk drive (HDD), the magnetization direction of a medium is reversed by a magnetic field generated from a recording head to perform write operation. In a conventional magnetic random access memory, a current is passed through an interconnect disposed near a magnetoresistive effect device to generate a current-induced magnetic field, which is applied to a cell to control the magnetization direction of the cell. These methods for controlling the magnetization direction by an external magnetic field (writing methods based on a current-induced magnetic field) have a long history and can be regarded as well-established techniques.
On the other hand, the recent progress in nanotechnology has enabled significant downscaling of magnetic materials. This has created a need to locally control magnetization at the nanoscale. However, a magnetic field intrinsically has the nature of spreading in space, and is difficult to localize. In selecting a particular bit or cell and controlling its magnetization direction, the problem of “crosstalk”, that is, extension of magnetic field to an adjacent bit or cell, becomes prominent with the downscaling of the bit or cell. On the contrary, downsizing the source of magnetic field to localize the magnetic field causes the problem of failing to generate a magnetic field enough to control the magnetization direction.
As a technique for solving these problems, the “spin injection induced magnetization reversal” is proposed, in which a current is passed through a magnetic material to induce magnetization reversal (e.g., F. J. Albert, et al., Appl. Phys. Lett. 77, 3809 (2000), hereinafter referred to as Non-Patent Document 1).
In the technique disclosed in Non-Patent Document 1, a spin injection current serving as a write current is passed through a magnetoresistive effect device to generate spin-polarized electrons, which are used for magnetization reversal. Specifically, the angular momentum of spin-polarized electrons is transferred to electrons in a magnetic material serving as a magnetic recording layer, and thereby the magnetization of the magnetic recording layer is reversed.
This type of technique for magnetization reversal directly driven by current (spin injection induced magnetization reversal technique) facilitates locally controlling magnetization at the nanoscale, and the value of the spin injection current can be decreased in accordance with the downscaling of the magnetic material. This facilitates realizing spin electronics devices such as hard disk drives and magnetic random access memories with high recording density.
Furthermore, there is a magnetic recording apparatus in which an alternating current is passed through a bit line or a word line to generate an alternating magnetic field (e.g., United States Patent Application Publication No. 2007/0047294, hereinafter referred to as Patent Document 1).
The magnetic recording apparatus disclosed in Patent Document 1 comprises a matrix of recording cells, each being addressable by a row (bit line) and a column (word line). Each magnetic cell has a ferromagnetic pinned layer, a barrier layer, and a ferromagnetic free layer (recording layer), and is subjected to writing in accordance with the orientation of current. Each magnetic cell is provided with a series-connected switching device (transistor). Each magnetic cell is connected to one bit line, and each switching device (transistor) is connected to one word line. The apparatus further includes a direct current power supply for passing a direct current at the time of recording, and an alternating current power supply for generating an alternating magnetic field.
Non-Patent Document 2: Shehzaad Kaka, et al., Journal of Magnetism and Magnetic Materials, Volume 286 (2005) p. 375